In modern biological analysis, various kinds of organic dyes are used. Among the most common types are fluorescent dyes. However, today more flexibility and demands are placed on these dyes. In addition, fluorescent dyes suffer from the disadvantage that the signal emitted by the fluorophors has a short lifetime which often necessitates continuous excitation by a laser. The requirement to excite the fluorophors at the same time as detecting the signal they emit in turn places considerable demands on the equipment needed to detect the fluorophors.
Nanocrystals of semiconducting materials, otherwise known in the art as quantum dots, have fascinated physicists, chemists and electronic engineers since the 1970s. The most striking feature of these materials is that their chemical and physical properties differ markedly from those of the bulk solid.[1] Now that their quantum size effects are understood, fundamental and applied research on these systems has become increasingly popular. An interesting application is the use of nanocrystals as luminescent labels for biological systems.[2-5] The quantum dots have several advantages over conventional fluorescent dyes: quantum dots emit light at a variety of precise wavelengths depending on their size and have long luminescent lifetimes.
While quantum dots possess these advantages over traditional fluorescent dyes, considerable challenges remain to be addressed concerning their stability and toxicity that limits their widespread use in biological systems. It also remains a problem to produce quantum dots that can be derivatised or coupled to biological species to make them useful in such studies.
Furthermore, numerous methods exist for the syntheses of semiconductor nanocrystals, but most processes are costly, require sophisticated equipment or extreme reaction conditions, and result in low product yields.[2,3,4,6] These synthetic methods are impractical for applications requiring larger quantities or higher concentrations of nanocrystals. Many of the conditions used in the manufacture and application of the quantum dots of the prior art have been incompatible with biological species.